Solid Fuel Devices for Fuel Cells

ABSTRACT

A fuel cartridge for a fuel cell, and a fuel cell design is presented wherein the system allows the intermittent use of the fuel in the cartridge. The fuel cell and cartridge provide improved design characteristics that improve the portability of fuel cells for use in portable electronic devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of copending application Ser. No.10/648,562 filed Aug. 26, 2003, and claims priority from applicationSer. No. 60/451,314, filed Feb. 28, 2003, the contents of which arehereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to fuel cells. Specifically, this inventionrelates to containers for holding solid fuels for fuel cells and devicesfor loading the containers.

BACKGROUND OF THE INVENTION

Fuel cells have developed as a method of generating electricity fromchemicals. Some early development focused on using hydrogen as a cleanfuel source for producing power. Work has been done on the storage andgeneration of hydrogen for use in fuel cells and is disclosed in U.S.Pat. No. 6,057,051, U.S. Pat. No. 6,267,229, U.S. Pat. No. 6,251,349,U.S. Pat. No. 6,459,231, and U.S. Pat. No. 6,514,478. Hydrogen is a highenergy, low pollution fuel, however, the storage of this fuel iscumbersome, both from an energy density and safety point of view.

The difficulty of storing hydrogen has led to looking at generatinghydrogen from more useful fuels. Liquid fuels containing a relativelyhigh amount of hydrogen that can be generated through reforming havereceived significant attention. Reforming of a fuel is expensive, andadds significantly to the complexity and size of a unit using fuel cellsfor power generation. Reformers and methods of reforming liquid fuelshave been developed, as shown in U.S. Pat. No. 4,716,859, U.S. Pat. No.6,238,815, and U.S. Pat. No. 6,277,330. Therefore, there is significantinterest in fuel cells that can use a hydrogen rich fuel that can beprocessed directly over a fuel cell electrode. This separates the fuelcells into two general categories: an indirect or reformer fuel cellwherein a fuel, usually an organic fuel, is reformed and processed toproduce a hydrogen rich, and substantially carbon monoxide (CO) freefeed stream to the fuel cell; and a direct oxidation fuel cell whereinan organic fuel is directly fed to the fuel cell and oxidized withoutany chemical reforming. Direct oxidation fuel cells can use either aliquid feed design or a vapor feed design, and preferably the fuels,after oxidation in the fuel cell, yield clean combustion products likewater and carbon dioxide (CO₂).

In early development of direct methanol fuel cells (DMFC), using gaseousmethanol required a high heat, which brought about the degradation ofthe fuel cell membranes. This led to the development of DMFCs usingmethanol in the liquid phase, as shown in U.S. Pat. No. 5,599,638, andU.S. Pat. No. 6,248,460. However, the liquid phase presents drawbacksalso, not the least of which is cross over of the membrane by themethanol and contamination of the cathode.

As with vapor phase fuel cells, liquid phase fuel cells also havehandling problems. Specific problems include some orientations of thefuel cells or portable devices allow liquid fuel to flow out of openingsfor releasing waste gases, and liquid fuel cells have the problem of thehigh concentration of liquid methanol permeating through to be oxidizedat the cathode which reduces fuel cell efficiency. Also, it would beconvenient for a user of a portable electronic device to have fuel incartridges and a device for handling the cartridges to limit thepossibility of fuel spillage, including leakage from any gaseous orliquid compounds generated.

SUMMARY OF THE INVENTION

The present invention is an apparatus for containing fuel and forcontrolling the release of the fuel from the apparatus. The apparatuscomprises a first compartment for holding a solid fuel, and a secondcompartment for holding a liquid activation agent. The first compartmentis in fluid communication with the second compartment, and thecommunication is controlled by a means for restricting the fluidcommunication between the first and second compartments. In oneembodiment, the apparatus further includes means for communicating withthe means for restricting the fluid flow between the first and secondcompartments

Another aspect of the invention is a receptacle for holding the fuelcontaining apparatus. The receptacle has a housing with a fuel cartridgetray slideably attached to the housing. The housing defines a sealablespace wherein the fuel cartridge resides, and includes a discharge portfor fuel from the cartridge to exit. The receptacle further includesmeans for communicating with the fuel cartridge.

A third aspect of the invention is a fuel cell. The fuel cell comprisesa system to bring a solid fuel in close proximity to the anodes. Thefuel cell comprises a housing with at least one membrane electrodeassembly (MEA) positioned within the housing, and with the anode sidefacing a space defined for a fuel cartridge within the housing. The fuelcell further includes a fuel cartridge tray for loading a fuel cartridgeinto the space within the housing, and a door to cover a fuel cartridgeinlet port. The door further includes a seal to provide a sealed spacein which a fuel cartridge facing an anode resides.

Other objects, advantages and applications of the present invention willbecome apparent to those skilled in the art after the following detaileddescription of the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram of a fuel cartridge with a valve for controlling themixing of water with the solid fuel;

FIG. 2 is a diagram of a second embodiment of a fuel cartridge;

FIG. 3 is a diagram of a third embodiment of a fuel cartridge;

FIG. 4 is a diagram of a fuel cartridge receptacle and holding device;

FIG. 5 is a side view of a fuel cartridge receptacle and holding devicewith the fuel cartridge in the receptacle tray; and

FIG. 6 is a diagram of a fuel cell in cross section showing the MEAs andthe fuel cartridge tray.

DETAILED DESCRIPTION OF THE INVENTION

Fuel cells are useful devices for supplying electronic devices with asteady source of electrical power. However, the fuel cells require asteady supply of fuel, and for portable electronic devices, a fuel thatis in a self-contained cartridge is desirable. The cartridge should alsobe attachable to the fuel cell in such a manner that a seal is providedsuch that the fuel cell anode compartment is sealed gas and liquid tightwhile open to the full in the cartridge.

In operation, the fuel cell generates electricity as long as fuel issupplied to the fuel cell. The fuel cell does not turn off when thepower is no longer needed, but continues to run when fuel is fed to thefuel cell. However, for many portable electronic devices, intermittentelectrical power is needed. Therefore, a means of controlling the flowof fuel to the fuel cell is needed, and a method of controlling theintermittent power required to be generated by a fuel cell is needed. Abattery provides the ability to use the electronic deviceintermittently, while not using power when the device is turned off.However, a battery also has a limited life and needs to be replaced orrecharged on a regular basis, and needs to be plugged into a constantstationary source of power for recharging. A fuel cell provides for alonger portable life but has less ability to automatically generate theamount of power needed at a given time. By providing a fuel cell with arechargeable battery, a portable electronic device can be runindefinitely with a supply of fuel cell cartridges. A fuel cell having aregulated flow of fuel to the fuel cell can provide intermittent powerto charge a battery. A control system providing a signal indicating thebattery's power level provides a signal to the fuel cell cartridge. Whenthe battery's power level is below a preset lower limit, a low powersignal is sent to the fuel cell cartridge. The fuel cell cartridgeactivates a means for allowing fuel to flow to the fuel cell. Inparticular, the fuel cell cartridge allows mixing of an activating agentwith a solid fuel to generate hydrogen. The activating agent continuesto mix with the solid fuel and the hydrogen continues to be generateduntil the fuel cell cartridge receives a signal indicating that thebattery's power is at or above a preset upper limit. When the battery'spower is at or above the preset upper limit, a signal is sent to thefuel cell cartridge, and the fuel cell cartridge deactivates the meansfor allowing fuel to flow to the fuel cell. Typically, the presetmaximum is below the total recharge of the battery to prevent wastingfuel by running the fuel cell when no more recharging is taking place.

Fuel cartridges are known and provide for charges of fuel to devices.Examples are found in U.S. Pat. No. 4,261,956; U.S. Pat. No. 6,267,299;U.S. Pat. No. 6,447,945; and U.S. Pat. No. 6,460,766, which areincorporated by reference in their entirety. Fuel cartridges currentlyhave the drawback of having no control over the amount of fueldelivered. This drawback limits the design of anodes in fuel cells andrequires ducting and valves within the fuel cell to direct and controlfuel flow. A feature of this invention is the ability to bring the solidfuel and fuel cell anode in close proximity, as well as controlling therelease of fuel to the anode.

The present invention comprises a fuel cartridge for use in a fuel cellthat provides for intermittent control of the flow of fuel to the fuelcell. The fuel cartridge holds a solid fuel, which when exposed to watergenerates a gaseous fuel for use in the fuel cell. One embodiment of thefuel cartridge is shown in FIG. 1, and comprises a housing 10 with afirst compartment 12, a second compartment 14, a conduit 16 connectingthe first 12 and second 14 compartments and providing fluidcommunication between the first 12 and second 14 compartments, and ameans 18 for restricting the fluid communication between the first 12and second 14 compartments disposed within the conduit. The firstcompartment 12 has an inlet port 13 in fluid communication with theconduit 16, and at least one outlet port 15 for the egress of hydrogen.The second compartment 14 has an outlet port 17 in fluid communicationwith the conduit 16. The use of a solid fuel for a fuel cell needs anactivating agent for the fuel to generate a gaseous component that isreactive at the anode. An example of an activating agent and solid fuelis water and lithium hydride solid fuel. The fuel cartridge receives asignal from a fuel cell controller. The signal triggers opening of therestriction means 18 in the conduit 16 allowing the activating agent toflow from the second compartment 14 to the first compartment 12. When anactivation agent, such as water is added to the solid fuel, the solidfuel reacts and releases hydrogen (H₂). The hydrogen exits the firstcompartment through a hydrophobic membrane 20 over the outlet ports 15of the first compartment 12. In the first embodiment, the fuel cartridgehas an overall rectangular prismatic shape and the first compartment 12within the cartridge also has a rectangular prismatic shape. The shapeof the cartridge may take a variety of forms, but it is envisioned thatthe preferred embodiment will be a relatively thin box having agenerally rectangular shape. An outlet port 15 for the first compartment12 comprises one of the faces of the first compartment 12. Thehydrophobic membrane 20 prevents moisture generated at the fuel cellanode from entering the solid fuel chamber of the fuel cartridge. In analternate embodiment, the first compartment 12 has two faces for outletports 15, and has a hydrophobic membrane 20 over each of the two facesof the first compartment 12, for a more rapid transfer of hydrogen outof the first compartment 12. In one embodiment, the means 18 forrestricting flow is a valve. Other restricting means include membraneshaving adjustable permeabilities, and flaps for shutting the conduit.

An alternate embodiment is a cylindrically shaped fuel cartridge, asshown in FIG. 2. The cartridge comprises a cylindrical housing 10 with afirst compartment 12 for holding a solid fuel, a second compartment 14for holding a liquid activating agent under pressure, a conduit 16providing fluid flow between the second compartment 14 and the firstcompartment, and a means 18 for restricting the flow of the liquidactivating agent from the second compartment 14 to the first compartment12. The hydrogen generated as a result of the liquid activating agentcontacting the solid fuel exits the first compartment 12 through anoutlet port 15 to a fuel conduit 22. The fuel conduit 22 includes anoutlet 21 covered with a hydrophobic membrane 20.

In one embodiment, the outlet 21 for the hydrogen includes a gasket (notshown) encircling the outlet 21. The gasket provides a seal between thefuel cartridge and a conduit connecting the fuel cartridge to the fuelcell, preventing leaks of hydrogen from a system of fuel cell and fuelcell cartridge. The gasket can be made of any elastomeric, orequivalent, material that is impermeable to hydrogen and water, and isdeformable such that when the cartridge is pressed into position, thegasket forms a seal. Materials for the gasket include for example,natural and synthetic rubbers, and soft plastics.

Alternate shapes and designs are possible and are intended to be coveredby the invention. The shapes and designs are subject to convenience andthe matching of the cartridge to a fuel cartridge receptacle componentof a fuel cell. Alternate shapes and designs also allow for multipleoutlets for the hydrogen from the first compartment.

The fuel for use in the fuel cell device is preferably a metal hydride,that reacts upon exposure to an activating agent releasing hydrogen.Solid fuels include, but are not limited to, lithium hydride (LiH),sodium hydride (NaH), potassium hydride (KH), beryllium hydride (BeH),magnesium hydride (MgH₂), calcium hydride (CaH₂), and mixtures thereof.The metal hydride can also be dispersed in carbon for providingstability of the fuel when the fuel is residing in the firstcompartment. While the invention is described with metal hydrides as apossible fuel, other fuels such as solid methanol fuels are applicable,and especially methanol fuels with adsorbents for adsorbing CO₂.

The solid fuel is in a water tight compartment and reacts with a liquidcomponent, or activating agent, that brings about the release ofhydrogen gas (H₂). Preferably the liquid is water, but the liquid canalso be aqueous solutions containing a dilute acid, or a dilute base.Acids include, but are not limited to hydrochloric acid (HCl), nitricacid (HNO₃), and sulfuric acid (H₂SO₄). Strong bases include, but arenot limited to, sodium hydroxide (NaOH) and potassium hydroxide (KOH).The aqueous solutions are preferably dilute solutions of the acids orbases, and have a concentration of no more than 0.1 molar.

Controlled release of the activating agent controls the rate of releaseof gaseous fuel to the fuel cell, which in turn controls the rate ofpower generation from the fuel cell. As the fuel cell generateselectrical power continuously with the feed of fuel, the fuel cell ispreferably designed to charge a battery, and shut off when the batteryreaches a preset level of charge. When the battery discharges to asecond preset level, the flow of fuel to the fuel cell is resumed to runthe fuel cell and recharge the battery. In this manner, only sufficientsolid fuel is used to meet the needs of the electronic device withoutcontinuous consumption of the solid fuel.

The controlled release is accomplished through a valve 18, or othermeans, for restricting the flow of the liquid activating agent to thesolid fuel. The valve 18, or other means, can open or closeelectronically or mechanically to allow the flow of the liquid through aconduit connecting the second compartment 14 to the first compartment12. Optionally, the cartridge further includes a connection means forcommunicating between a controller (not shown) and the fuel cartridgevalve 18. The cartridge includes an operator for opening and closing therestriction means, or valve 18. The generator receives a signal to openor close the valve through a communication means. The communicationmeans allows communication between the cartridge and the fuel cell or afuel cell controller providing the signal to the operator for opening orclosing the valve. Preferably, the cartridge includes an electronic bushaving contacts with a complementary system enabling electroniccommunication between the controller and the valve 18. Although anelectronic bus is preferred, a mechanical linkage is also envisioned bythis invention, and intended to be covered.

The liquid activating agent flows under pressure from the secondcompartment 14 to the first compartment 12. The housing 10 can beoriented such that the outlet to the second compartment 14 is alwaysoriented at the bottom, or at a lower region, of the compartment.However, an alternate means for maintaining pressure and keeping theliquid under pressure, and enabling the liquid to flow out of thecompartment outlet without pressurizing gas escaping is to affix aflexible bladder (not shown) within the second compartment 14. Theflexible bladder separates the liquid and pressurizing gas, and expandsas the liquid exits the compartment 14. The bladder is affixed to aposition within the compartment, such that the bladder when expandeddoes not cover the outlet port of the second compartment 14. This allowsfor any orientation of the cartridge.

The fuel cartridge further includes means for communicating between thefuel cartridge and the fuel cell. An example includes electricalcontacts, such that when the fuel cartridge is in a receptacle and thereceptacle is in a closed position, then contact is made between theelectrical contacts on the cartridge and contacts in the receptacle. Thereceptacle may be a part of a fuel cell, or a device attached to a fuelcell and provide a proper connection between the fuel cell or a fuelcell controller and the fuel cartridge. The contacts allow forelectrical communication between the fuel cell and the fuel cartridge.The electrical communication is for transmitting a signal to the fuelcartridge valve 18, indicating that the valve should be in an open orclosed position. Alternately, the means for communicating between thefuel cartridge and the fuel cell receptacle may be a mechanical linkage.

An alternate embodiment of the present invention includes an array ofcontainers within a cartridge, as shown in FIG. 3. The fuel cartridgecomprises a housing 10 for holding a plurality of containers 24, orchambers, with each container holding a preset amount of solid fuel.Each container 24 includes an opening for the entrance of an activatingagent, i.e. moisture, and the exit of gaseous fuel for the fuel cell.The opening of each container is sealed with a cover 25 that isremovable upon receiving an appropriate signal. The cartridge furtherincludes a means 26 for selecting an individual container to beunsealed.

The means 26 can be any switching means, such as a small computer chip,for sending a signal to an individual container 24. Preferably, thecover 25 is opened through means such as an electrical current thatheats the cover and opens the container. The means for opening the covermay be an electrical resistance element for generating heat, or a smallamount of a chemical that upon initiation with an electrical currentreacts to heat and open the cover.

Alternately, the cover may include a bimetallic material thatpreferentially bends in one direction upon heating. An alternate meansfor sealing the cover to the container is the use of a low temperatureadhesive, such that upon heating the adhesive strength is reducedsufficiently to open the cover. Still another alternate means forsealing the cover is to use a low melting point wax or thermoplasticmaterial that can be heated and melted to open the container.Preferably, the low melting point wax or thermoplastic will melt at atemperature above the operating temperature of the electronic device. Apreferred temperature range is from about 100° C. to about 200° C.

While a cartridge as shown in FIG. 3 is a rectangular grid array, thehousing 10 and array of cylinders are not limited to those shown. Thehousing may include a cylindrical shape with the containers formed in aspiral wound array, or the cartridge can be of any design, butpreferably is a design that is convenient and adapted to an appropriatefuel cartridge receptacle in a fuel cell.

Apparatuses of the type presented in FIG. 3, are also applicable as fuelcartridges for DMFCs. Solid fuels that work with this apparatus includefuels for generating hydrogen, as well as fuels for generating gaseousmethanol. When the fuels include solid fuels for generating methanol,the cartridge may further include an adsorbent compartment. Theadsorbent compartment contains a material for adsorbing carbon dioxidegenerated at the anode of the fuel cell.

A further part of this invention includes an apparatus, or receptacle,for holding a fuel cartridge. The fuel cartridge for use in a fuel cellis sized and shaped to fit such a fuel cartridge receptacle. One suchreceptacle 30 is shown in FIG. 4. The receptacle 30 includes a housing32 having an insertion port 34 for inserting a fuel cartridge (notshown), and at least one discharge port 36 for the exit of a gaseousfuel from the fuel cartridge. In one embodiment of this invention, thereceptacle 30 is shaped to hold a rectangularly shaped fuel cartridge.The apparatus includes a fuel cartridge tray 38 for holding the fuelcartridge. The fuel cartridge tray 38 is slideably affixed to thehousing 32 and moves between an open position, for inserting a newcartridge or removing a spent cartridge, and a closed position whereinthe tray 38 resides within the housing 32. The fuel cartridge receptacle30 further includes a means for pressing the outlet ports of the fuelcartridge against the discharge ports 36 of the receptacle 30. Thereceptacle 30 further includes a means 40 for controlling the openingand closing of the valve 18 within the fuel cartridge.

In one embodiment, as shown in FIG. 5, which shows a cartridge 10positioned in the tray 38, the tray 38 in the receptacle 30 slides alongguides 42 to ensure proper positioning of the tray 38 and cartridge 10.The tray can move in and out of the receptacle manually, or preferablywith an automated motor, drive, and control system. Automated motor,drive, and control systems are known as shown in U.S. Pat. No.4,722,078; U.S. Pat. No. 5,572,498; U.S. Pat. No. 6,452,893; U.S. Pat.No. 6,477,133; U.S. Pat. No. 6,490,238; and U.S. Pat. No. 6,510,122,which are incorporated by reference. An automated system provides forproper positioning and a more consistent operation. The receptacle has adoor 44 that opens when the tray 38 extends out of the receptacle 30,and closes when the tray 38 retracts into the receptacle 30. The door 44is affixed to the tray 38 and is positioned on the tray 38 to cover theinsertion port 34 when the tray 38 is retracted into the receptacle 30.Optionally, the door 44 is attached with a hinge to the receptacle andautomatically opens when the tray 38 extends out of the receptacle 30and automatically closes when the tray 38 retracts into the receptacle30. The door 44 may include a spring to automatically close the door 44.

The tray 38 consists of a rigid framework in which the fuel cartridge isplaced. The tray 38 has an open structure which allows for free flow ofgas out of the exit ports of the fuel cartridge 10. Preferably, the tray38 has a snap-in configuration to position the cartridge 10 moreprecisely when the cartridge 10 is drawn into the receptacle 30. Asnap-in configuration is a design wherein the cartridge is shaped to fitwith a relatively close tolerance into the cartridge tray. The cartridgefurther has a slot or protrusion that fits into a correspondingprotrusion or slot in the tray respectively, such that when thecartridge is placed in the tray the corresponding slot and protrusionsnap together.

In one embodiment, the door 44 when closed is sealed to isolate the fuelcartridge 10 from the exterior of the fuel cartridge receptacle 30. Inthis embodiment, a seal is affixed around the edge of the door 44, orthe edge of the insertion port 34. The seal is comprised of anelastomeric, or other, material that is deformable under the slightcompression when the door 44 is closed over the insertion port 34.Optionally, the door 44 includes a latch (not shown) for maintaining thedoor 44 in a closed position when the door 44 is closed. Release of thelatch may either be a manual or an automated process when the door 44 isopened. When the door 44 is closed and sealed, the fuel cartridge canrelease fuel to the receptacle discharge port 36. This enables astructure that has a closed and sealed compartment in which the fuelcartridge is placed.

In an alternate embodiment, the fuel cartridge includes an elastomericseal in a surrounding relationship to the cartridge outlet. Thecartridge outlet is covered with a hydrophobic membrane 20, andtherefore the seal surrounds the membrane 20. The cartridge outlet issized and shaped to conform to the discharge port 36 of the fuelcartridge receptacle 30. The cartridge is inserted into the tray 38 andis brought into the receptacle. The cartridge is then pressed againstthe discharge port 36 of the fuel cartridge receptacle 30 forming anairtight seal. The means for pressing the cartridge can be manual orautomatic. Means include, but are not limited to, guides in thereceptacle for guiding the tray into position, a levered means forpressing the cartridge and tray against the discharge port when the trayis retracted into the receptacle, and a motor that is activated when thetray is in the retracted, or closed, position and then presses thecartridge against the discharge port 36.

The fuel cartridge receptacle 30 can be part of a fuel cell. Thisstructure enables the positioning of the fuel in close proximity to theanode in a fuel cell and minimizes the creation of ducts or channels todirect gaseous fuel over the fuel cell anodes.

In one embodiment, the invention includes a fuel cell, as shown in FIG.6, and is shown in cross section. The fuel cell comprises a housing 50and within the housing a membrane electrode assembly (MEA) 52 isdisposed. An MEA comprises an anode, a cathode, and an ion conductingmaterial positioned between the anode and cathode forming a layeredstack. The fuel cell housing 50 includes a cartridge tray port anddefines a space for a fuel cartridge. A fuel cartridge tray 38 isattached to the fuel cell in slideable manner, and can move between anopen position and a closed position through the cartridge tray port. Thecartridge tray 38 can receive a fuel cartridge 10 when in the openposition, and bring the fuel cartridge into the defined space when inthe closed position. The MEA 52 is positioned within the defined spaceand with the anode side of the MEA facing the space defined for the fuelcartridge 10. This brings the fuel in close proximity to the anode.

The fuel cell further includes a door 44 for covering the cartridge trayport. The door 44 seals the defined space when the door 44 is closed. Toform the seal a sealing material 54 such as a gasket is positionedaround the edge of the door 44 can contacts the housing to form a seal.Alternatively, the seal 54, or gasket, can be positioned on the housing50 around the cartridge tray outlet, forming a seal when the door isclosed. In one embodiment, the door 44 is affixed to the cartridge tray38, and opens when the cartridge tray 38 moves to the open position, andcloses when the cartridge tray 38 is retracted to the closed position.Alternately, the door is hingeably attached to the housing and swingsopen and closed over the cartridge tray outlet. The door can includesprings to provide sufficient tension to hold the door against thehousing in a sealed condition.

The gasket can be any material that is impermeable to air, and issufficiently flexible to form a seal when the door is pressed againstthe housing. Materials for the gasket include, but are not limited to,deformable thermoplastics such as polyethylene, polypropylene,co-polymers of ethylene and propylene, co-polymers of acrylonitrile andbutadiene, fluorocarbon elastomers, polyurethane elastomers, silicone,synthetic and natural rubbers, and fabrics impregnated with a materialto make the fabric impermeable to air.

The fuel cell is preferably of a size and shape convenient for use in aportable electronic device. A preferred shape is a rectangular prism, orbox shape, with dimensions of a height of less than 4 cm, a width fromabout 5 to 15 cm, and a depth from about 5 to 30 cm. The box shape is aconvenient shape to fit within a laptop computer, and preferably has asmall height to conform to the size limitations of a laptop computer.

Preferably, the fuel cell comprises two MEAs positioned within thedefined space and in opposite orientations, one on top and one on thebottom, with their anode sides facing the cartridge tray. This providesa large area for the anodes. A preferred fuel cartridge has a large exitport on the top of the cartridge and a large exit port on the bottom ofthe cartridge with each port covered by a hydrophobic membrane. Thisconfiguration provides a relatively large anode surface area exposed inclose proximity to the fuel. The preferred embodiment further includes aseal around the door to provide a sealed fuel chamber with a minimum ofair space around the cartridge. While the fuel cell and fuel cellcartridge are described in an orientation with a “top” and a “bottom”,the use of solid fuel permits any configuration and is not restricted tosuch an orientation.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiments, but, on the contrary, is intended to covervarious modifications and equivalent arrangements within the spirit andscope of the appended claims which scope is accorded the broadestinterpretation so as to encompass all such modifications and equivalentstructures as is permitted under the law.

1. A solid fuel cartridge for use in a fuel cell comprising; a pluralityof solid fuel containers, wherein each container comprises: a housinghaving at least one opening; a cover covering the opening in a sealingmanner; means for selectively unsealing the cover from the housing; andmeans for switching between the unsealing means for one container to theunsealing means for another container.
 2. The cartridge of claim 1wherein the means for selectively unsealing the cover comprises anelectrical heating element.
 3. The cartridge of claim 1 wherein theplurality of solid fuel containers are in a rectangular grid array or aspiral wound array.
 4. The cartridge of claim 1 wherein the cover ismade of a bimetallic material that springs open upon heating.
 5. Thecartridge of claim 1 further comprising: a cover for each solid fuelcontainer, where each cover comprises a flexible material; and anadhesive for sealing the cover over the opening, wherein the adhesivewhen heated loses its adhesive power.
 6. The cartridge of claim 1wherein the cover is a low melting point wax or thermoplastic.
 7. Thecartridge of claim 6 wherein the low melting point wax or thermoplasticmelts at a temperature between about 100° C. and about 200° C.
 8. Thecartridge of claim 1 wherein the means for selectively unsealing thecover is an electrical resistor for generating heat to melt the cover.9. The cartridge of claim 1 wherein the switching means is an electronicswitch.
 10. The cartridge of claim 1 further comprising an adsorbentcompartment and containing a material for adsorbing carbon dioxide.